Export ServiceState#DataRegState into TelephonyProvider

Add test case to make sure notifyChange was called by
notifyChangeForSubId and notifyChangeForSubIdAndField
when dataRegState changes.

Bug: 182601774
Test: atest com.android.phone.ServiceStateProviderTest
Change-Id: I30f4b3f53daa311ef2526b9f5aceed2099df6da0
2 files changed